Thioester protein crosslinks

[https://en.wikipedia.org/wiki/Thioester Thioester bonds] between cysteine and glutamine sidechains can form covalent cross-links between polypeptide chains. Thioester bonds are one way that ubiquitin may be attached to proteins ([https://en.wikipedia.org/wiki/Ubiquitin ubiquitinylation]; see also [[Ubiquitin and Ubiquitination]]). Thioester bonds in [https://en.wikipedia.org/wiki/Complement_system complement proteins] C3 and C4 are involved in tagging pathogens for destruction by the immune system, via the alternate complement activation pathway. Thioester bonds occur in thioester domains (TED) of Gram-positive bacteria, where they are thought to mediate covalent adhesion of bacteria to host cells<ref name="slipknot">PMID: 30052296</ref>. Many surface proteins of Gram-positive bacteria are predicted to contain TED as well as [[isopeptide bond|isopeptide]] and ester cross-links. This family of proteins is termed <b>TIE proteins</b> for thioester, isopeptide, ester proteins<ref name="slipknot" />.